Fetal heart monitors employ ultrasound transducers for measuring physiological parameters of the heart of an unborn child. In some circumstances, abdominal fat may increase a distance between the ultrasound transducer and the fetal heart being monitored. Increasing the penetration depth of ultrasound pulses to accommodate this larger distance may decrease signal-to-noise ratio and may undesirably result in the ultrasound transducer picking up a signal from the maternal abdominal vessels in addition to or in place of a signal from the fetal heart rate.